1. Field of the Invention
The present invention relates to an optical fiber and, more particularly, to an optical fiber applicable in long-distance optical communication networks.
2. Description of the Related Art
In an effort to cope with an ever-increasing demand for higher capacity and speed, optical communication systems—namely, a WDM (wavelength division multiplex) technique that can perform a large-capacity transmission at high speed—are being deployed. The WDM systems may be classified into DWDM (dense wavelength division multiplex) systems and CWDM (coarse wavelength division multiplex) systems.
The optical communication networks utilizing the WDM mode are classified into access networks, metro-access networks, metro-core networks, long-haul networks, and ultra long-haul networks depending on the transmission distance. The access networks represent short-distance optical communication networks, while the metro and long-haul networks are long-distance optical communication networks. Specifically, the access networks are used for a distance range of 1–5 km; the metro-access networks for 20–100 km; the metro-core networks for 100–300 km; the long-haul networks for 300–1000 km; and the ultra long-haul networks for 1000 km or more.
Optical fibers used in long-distance optical communication networks in the range of hundreds of kilometers, such as metro and long-haul networks, include a core having a high refractive index, a clad having a low refractive index, and an optional ring region positioned between the core and the clad with a lower refractive index than that of the core. For economic reasons, the conventional long-distance optical communication networks use optical fibers having a dispersion value of −7 to −8 ps/nm/km at a wavelength of 1550 nm.
However, the optical fibers having a dispersion value of −7 to −8 ps/nm/km at a wavelength of 1550 nm tend to experience a degraded transmission efficiency due to dispersion at a transmission rate of 2.5 Gbps. Furthermore, they are not suitable for use in metro networks, which have a transmission distance of 100 km or more and a transmission rate of 10 Gbps, due to this excessively negative dispersion value.
In an effort to solve the above problem, it is proposed to use optical fibers having a large dispersion gradient in the long-distance optical communication networks with a transmission distance of 100 km or more. However, this proposal has a problem in that, although the dispersion characteristics are suitable for metro networks for 200 km or less, it has a limited transmission distance due to a dispersion phenomenon in the case of long-haul networks for long-distance transmission of 200 km or more. Moreover, a nonlinear phenomenon, such as FWM (four-wave mixing), occurs when the optical fibers have a small dispersion-gradient value at a wavelength of 1550 nm, and have a limited transmission distance due to an increased dispersion, which occurs when the dispersion gradient value is large.